Immune functions of liver natural killer T (NKT) cells induced by the synthetic ligand ␣-galactosylceramide enhanced age-dependently; hepatic injury and multiorgan dysfunction syndrome (MODS) induced by ligand-activated NKT cells were also enhanced. This study investigated how aging affects liver innate immunity after common bacteria DNA stimulation. Young (6 weeks) and old (50-60 weeks) C57BL/6 mice were injected with CpG oligodeoxynucleotides (CpG-ODN), and the functions of liver leukocytes were assessed. A CpG-ODN injection into the old mice remarkably increased tumor necrosis factor (TNF) production in Kupffer cells, and MODS and lethal shock were induced, both of which are rarely seen in young mice. Old Kupffer cells showed increased Toll-like receptor-9 expression, and CpG-ODN challenge augmented TNF receptor and Fas-L expression in liver NKT cells. Experiments using mice depleted of natural killer (NK) cells by anti-asialoGM1 antibody (Ab), perforin knockout mice, and mice pretreated with neutralizing interferon (IFN)-␥ Ab demonstrated the important role of liver NK cells in antitumor immunity. The production capacities of old mice for IFN-␥, IFN-␣, and perforin were much lower than those of young mice, and the CpG-induced antitumor cytotoxicity of liver NK cells lessened. Lethal shock and MODS greatly decreased in old mice depleted/deficient in TNF, FasL, or NKT cells. However, depletion of NK cells also decreased serum TNF levels and FasL expression of NKT cells, which resulted in improved hepatic injury and survival, suggesting that NK cells are indirectly involved in MODS/lethal shock induced by NKT cells. Neutralization of TNF did not reduce the CpG-induced antitumor effect in the liver. Conclusion: Hepatic injury and MODS mediated by NKT cells via the TNF and FasL-mediated pathway after CpG injection increased, but the antitumor activity of liver NK cells decreased with aging. (HEPATOLOGY 2008;48:1586-1597.)
U nmethylated CpG oligodeoxynucleotide (CpG-ODN) motifs (GACGTT for mice and GTCGTT for humans) in bacterial DNA have a potential to strongly activate the innate immune system. 1,2 Unmethylated CpG motifs are common in bacterial DNA, whereas they are underrepresented and methylated in vertebrate DNA. 3 This difference in the frequency of unmethylated CpG dinucleotides between bacterial and vertebrate DNA provides a structural characteristic through which vertebrate immune cells may detect and respond to bacterial infection. CpG mimics the stimulatory effect of DNA of either gram-negative or gram-positive bacteria. 1,4 The Toll-like receptor (TLR) family is a phylogenetically conserved mediator of innate immunity that is essential for microbial recognition. 5 Lipopolysaccharide (LPS), a gram-negative bacterial component, and bacterial DNA (or CpG) engage TLR4 6 and TLR9, 7 respectively. A CpG challenge, similarly to an